High strength steel

This application is a divisional of U.S. application Ser. No. 11/375,186 which is a continuation-in-part of U.S. application Ser. No. 11/092,434, filed Mar. 29, 2005, which claims priority to U.S. provisional application No. 60/557,367, filed Mar. 29, 2004, all of which are relied on and incorporated by reference.

Articles such as anchor bolts are used in the utility industry to secure transmission poles to concrete bases. Such articles require a strong material that exhibits good low temperature impact strength. One suitable material for such articles is steel having a minimum Charpy v-notch impact strength at 20F of 15 Ft-1b and minimum yield strength of 75,000 psi. Such steels are typically manufactured according to a process that involves normalizing the steel in a furnace at high temperatures, followed by a separate, high temperature tempering treatment, to ensure production of steels that consistently have the required mechanical properties.

Advantageous steel compositions are described that include iron as the main constituent and the following additional elements:

(a) about 0.25-0.37% (preferably about 0.30-0.34%, more preferably about 0.30-0.32%) by weight carbon;

(b) about 1.20-1.55% (preferably about 1.25-1.50%, more preferably about 1.35-1.45%) by weight manganese;

(c) about 0.1-0.15% (preferably about 0.11-0.14%) by weight vanadium;

(d) about 0.20-0.40% by weight nickel;

(e) about 0.20-0.50% by weight silicon;

(f) about 0.30-0.45% by weight copper; and

(g) about 0.017-0.025% (preferably about 0.018-0.022%, more preferably about 0.019-0.021%) by weight nitrogen. The composition may also include one or more of the following elements:

(h) up to about 0.30% (preferably up to about 0.25%, more preferably up to about 0.20%) by weight chromium;

(i) up to about 0.035% (preferably up to about 0.025%, more preferably up to about 0.020%) by weight phosphorus;

(j) up to about 0.04% by weight sulfur (preferably up to about 0.02%);

(k) up to about 0.06% by weight tin; and/or

(l) up to about 0.06% (preferably up to about 0.04%) by weight molybdenum.

In some embodiments, Ti, Nb and Al can be present individually or in combination in amounts of up to 0.025% by weight Ti, up to 0.025% by weight Nb and up to 0.04% Al.